The present invention generally concerns switches. More specifically, the present invention concerns microelectromechanical switches that are capable of switching at low actuation voltages.
Switching operations are a fundamental part of many electrical, mechanical, and electromechanical applications. Microelectromechanical systems (MEMS) for switching applications have drawn much interest especially within the last few years. Products using MEMS technology are widespread in biomedical, aerospace, and communication systems. Recently, the MEMS applications for radio frequency (RF) communication systems have gained even more attention because of the MEMS""s superior characteristics. RF MEMS have advantages over traditional active-device-based communication systems due to their low insertion loss, high linearity, and broad bandwidth performance.
Known MEMS utilize cantilever switch, membrane switch, and tunable capacitors structures. Such devices, however, encounter problems because their structure and innate material properties necessitate high actuation voltages to activate the switch. These MEMS devices require voltages ranging from 10 to 100 Volts. Such high voltage operation is far beyond standard Monolithic Microwave Integrated Circuit (MMIC) operation, which is around 5 Volts direct current (DC) biased operation.
Known cantilever and membrane switches are shown in FIGS. 1 and 2 in resting and excited positions. FIG. 1A shows a cantilever switch in a resting position with a cantilever portion a distance hA away from an RF transmission line to produce an off state since the distance hA prevents current from flowing from the cantilever to the transmission line below it. To turn the switch on, a large switching voltage, typically in the order of 28 Volts, is necessary to overcome physical properties and bend the metal down to contact the RF transmission line (FIG. 1B). In the excited state, with the metal bent down, an electrical connection is produced between the cantilever portion and the transmission line. Thus, the antilever switch is on when it exists in the excited state.
In addition, referring to FIGS. 2A and 2B, a known membrane switch is shown in a resting (FIG. 2A) and an excited (FIG. 2B) position. When the membrane switch exists in the resting position, current is unable to flow from the membrane to an output pad and the switch is off. Like the cantilever switch, a high actuation voltage, typically 38 to 50 Volts, is necessary to deform the metal and activate the switch. In the excited state, the membrane is deformed to contact a dielectric layer on the output pad and thereby electrically connect the membrane to the output pad to turn the switch on. These designs also require a relatively high voltage.
There is a need for an improved apparatus and method which addresses some or all of the aforementioned drawbacks of known switches. Importantly, a new apparatus and method should overcome the need for high actuation voltages. In addition, the apparatus and method should overcome the limitations of traditional active-device-based switches.
Such needs are met or exceeded by the present apparatus and method for switching. The present system controls the flow of a signal with a metal or other suitable conductive pad that moves freely up and down within brackets, without the need for deformation. The pad electrically grounds a signal when the pad is located in a relaxed position (contacts closed) and allows the signal to pass when located in a stimulated position (contacts open). The present invention includes electrodes that move the pad up and down with a low actuation voltage compared to known devices. The pad is not bent by the actuation voltage to make contact.
More specifically, in a preferred embodiment, the present invention controls the flow of signals by either shorting the signals to ground or allowing the signal pass through a signal line. The switch contains coplanar or other waveguides including the signal line and ground planes. The metal pad responds to an actuation voltage to electrically connect the signal line and the ground planes when the metal pad is in the relaxed position. When not located in the relaxed position, the switch allows signals to flow through the signal line unimpeded. Brackets guide the metal pad as the metal pad moves between the relaxed position and a stimulated position in response to the actuation voltage.